Boats powered by inboard engines discharge the exhaust gases, or fumes, from the engine to the outside environment through an exhaust pipe. The exhaust pipe normally projects outwardly through the boat transom, or at a location on the hull near the transom, in order to discharge the gases behind the boat. The exhaust pipe outlet is usually located above the water line of a moving boat in order to discharge the gases above the water surface to avoid back pressure.
A primary disadvantage with conventional marine exhaust systems is that the exhaust pipe discharges the fumes in the immediate locale of the boat transom. Depending on the shape and size of the transom, speed of the boat, and location of the exhaust pipe outlet, portions of the exhaust fumes can remain near the transom. Furthermore, the fumes can even follow a moving boat due to a partial vacuum "stationwagon effect" that exists behind moving boats. The exhaust fumes which come into contact with the boat, especially those from diesel combustion engines, can severely soil the boat surfaces, particularly the transom, resulting in lost time and cleaning expenses to restore the cleanliness of the boat.
The following patents show devices intended to reduce contact of exhaust gases with adjacent surfaces of the boat or its occupants or to reduce exhaust noises: U.S. Pat. Nos. 4,714,443, 3,907,061, 3,568,672, 3,084,651, 2,859,830, 2,522,883, 1,198,274, 1,031,943, and 987,130.